For more than a century after the republic’s founding in the 1780s, American law reflected the ideal that the commons—the public domain—should be turned into private property. As Americans became concerned about resource scarcity, waste, and monopolies at the end of the 19th century, reform-minded bureaucrats and scientists convinced Congress to maintain in perpetuity some of the nation’s land as public. This shift offered a measure of protection and an alternative to private property regimes. The federal agencies that primarily manage these lands today—U.S. Forest Service (USFS), National Park Service (NPS), U.S. Fish and Wildlife Service (USFWS), and Bureau of Land Management (BLM)—have worked since their origins in the early decades of the 20th century to fulfill their diverse, competing, evolving missions. Meanwhile, the public and Congress have continually demanded new and different goals as the land itself has functioned and responded in interdependent ways. In the mid-20th century, the agencies intensified their management, hoping they could satisfy the rising—and often conflicting—demands American citizens placed on the public lands. This intensification often worsened public lands’ ecology and increased political conflict, resulting in a series of new laws in the 1960s and 1970s. Those laws strengthened the role of science and the public in influencing agency practices while providing more opportunities for litigation. Predictably, since the late 1970s, these developments have polarized public lands’ politics. The economies, but also the identities, of many Americans remain entwined with the public lands, making political standoffs—over endangered species, oil production, privatizing land, and more—common and increasingly intractable. Because the public lands are national in scope but used by local people for all manner of economic and recreational activities, they have been and remain microcosms of the federal democratic system and all its conflicted nature.